JPH0423504B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnet field type DC motor in which a permanent magnet is used as a main pole and auxiliary poles are arranged adjacent to each other on the radial surface of the main pole, and a method for manufacturing the same.

In a DC machine used for a starting motor of an internal combustion engine, etc., as shown in Fig. 1, a yoke 2 of a stator 1 is
It is known that torque characteristics can be improved by attaching a main magnetic pole 3 made of a permanent magnet and an auxiliary magnetic pole 4 made of a piece of soft iron so as to be adjacent to each other in the circumferential direction on the annular inner diameter surface of the magnet. In such a known magnet field type DC machine, the auxiliary magnetic pole 4 is generally formed by drawing or cold forming a soft iron material, and due to the material, it is difficult to obtain sufficient machining accuracy in machining to desired dimensions. There are no particular difficulties.

However, ferrite magnets, which are generally used as permanent magnets for the main magnetic pole 3, are extremely hard and brittle, as is also known from the name ceramic magnets, so they cannot be cut with a cutting tool coated with diamond and abrasive grains. Mainstream and requires special processing. By such special processing, the outer and inner diameter surfaces of the main pole 3 are finished to the desired dimensions before the main pole 3 is attached to the yoke 2, and then the outer and inner diameter surfaces are also finished to the desired dimensions. The auxiliary magnetic poles 4 and the auxiliary magnetic poles 4 are fixed adjacent to each other on the inner diameter surface of the yoke 2.

However, due to machining errors caused by the special machining described above, tolerances on the outer diameter surface and inner diameter surface of the main magnetic pole 3, as well as tolerances such as waviness and cylindricity, are accumulated, and the main magnetic pole 3
Since there is a possibility that the inner diameter of the armature 5 becomes smaller than the outer diameter of the armature 5 and it becomes impossible to insert the armature 5 into the stator 1, the main magnetic pole 3 is
The inner diameter must be made extra large. This causes the air distance d between the outer diameter surface of the armature 5 and the inner diameter surface of the main pole 3 to become an excessive value exceeding the original minimum distance necessary to prevent contact between the two surfaces.
As is well known, an increase in the air distance d means an increase in the magnetic resistance of the air distance d, which accounts for most of the total magnetic resistance in the magnetic circuit excited by the field pole. The magnetic flux density or the magnetic flux in the magnet decreases inversely proportionally, lowering the torque.
In other words, the torque characteristics improved by the addition of the auxiliary magnetic pole are largely lost due to the decrease in the number of magnetic fluxes due to the increase in the air distance. Furthermore, the effect of reducing the magnetizing effect of the armature reaction due to this auxiliary magnetic pole installation method is also largely canceled out due to the decrease in magnetic flux density due to the increase in air distance, and there is a risk that the permanent magnet will be demagnetized by addition. be.

The object of the present invention is to obtain a stator structure that solves the conventional difficulties of the DC machine field system as described above.

An embodiment of the present invention will be described below with reference to FIG. Reference numerals 1 to 5 in the figure indicate the same parts as those in FIG. First, stator 1 yoke 2
The inner diameter surface of the auxiliary magnetic pole 4 made of soft iron material by drawing or cold forming, and the main magnetic pole 3 made of fired ferrite magnet material are each individually cut to have the outer diameter surface and inner diameter surface cut to a predetermined size. Finish it to the specified dimensions by grinding or grinding.

Next, the finished main magnetic pole 3 and auxiliary magnetic pole 4 are placed adjacent to each other along the direction of rotation of the armature 5, and their respective outer diameter surfaces are fixed to the inner diameter surface of the yoke 2 using an adhesive or the like. A cross section of the stator 1 having the field poles formed in this way is shown in _FIG . ) is D, the inner diameter of the auxiliary magnetic pole 4 is D _s , and the outer diameter of the armature is D _a
, the predetermined sky distance is d, and D _a +2d=
Let D _p , D _p −D/2=δ.

After the main magnetic pole 3 and the auxiliary magnetic pole 4 are attached to the yoke 2 adjacent to each other as described above, the inner diameter surface of the main magnetic pole 3 is ground by a thickness δ using a special tool to which the diamond abrasive grains are attached. Accordingly, the main magnetic pole 3
The inner diameter D of the main pole 3 is ground to D _p , and the difference between the ground inner diameter D _p of the main pole 3 and the outer diameter D _a of the armature 5, that is, the empty distance, is D _p − D _a / according to the above relationship. 2=d.

In addition, the auxiliary magnetic pole 4 is machined before the installation process from the yoke 2 so that its inner diameter D _s is the same as that of the main magnetic pole 3 after the above-mentioned grinding.
By making the inner diameter slightly larger than the inner diameter of the auxiliary magnetic pole 4, it is possible to avoid grinding the finished, relatively soft soft iron surface of the auxiliary magnetic pole 4 with the grinding tool of the main magnetic pole 3. It is possible to prevent the tool from being damaged due to clogging with soft iron cutting powder.

As mentioned above, before attaching the main magnetic pole 3 to the yoke 2, by finishing its inner diameter D smaller than the final finished dimension _Dp by the previously predicted grinding thickness 2δ, the main magnetic pole 3 can be attached to the yoke 2. When the subsequent grinding thickness reaches δ, the air distance to the armature 5 becomes a predetermined distance d. In other words, when the main magnetic pole 3 is attached to the yoke 2, due to the difficulty in machining the permanent magnet material, it is difficult to determine how the finish tolerances of each part dimension and the tolerances such as cylindricity are accumulated due to the machining before installation. However, if the inner diameter surface of the main magnetic pole 3 is machined before installation so that the inner diameter D takes into account the grinding thickness δ that can accommodate this total tolerance volume, then the inner diameter D of the main magnetic pole 3 can be changed after installation. When the diameter is expanded to D _p by grinding, the air distance between the inner diameter surface of the main pole 3 and the surface of the armature 5 inevitably matches the initially set value d.

In the present invention, as described above, regardless of the accumulation of manufacturing and installation tolerances of the main pole 3,
The distance d could always be accurately matched to the desired set value, and an undesired increase in the d value could be reliably prevented. Although the above embodiment shows an example in which the inner diameter surface of the main pole is machined, if the machining accuracy of the magnet is improved, the air distance can be accurately obtained without machining the inner diameter.

As a result, the decrease in magnetic flux density due to the increase in air distance as described in the conventional example,
The problems associated with this, such as a decrease in output or torque, have been solved, and the magnetizing effect of the armature reaction caused by the auxiliary magnetic pole 4 is canceled out by the demagnetizing effect due to the increase in air distance, resulting in irreversible demagnetization. It could have been prevented.

As an example of a DC machine according to the present invention, the outer diameter of the yoke 2 is 68 mm, the core thickness of the armature 5 is 45 mm, and the dimensional difference between the inner diameter D _p of the main magnetic pole 3 and the inner diameter D _s of the auxiliary magnetic pole 4 is 0.1 mm. According to the experimental results, by reducing the air distance d from the conventional 0.5 to 1.0 mm to 0.4 to 0.5, the output was improved by increasing the magnetic flux density.
The result was an improvement of 6.7%, and an improvement in demagnetization resistance of 7%.

Note that FIG. 2 shows an analytical diagram of the excitation operation of a permanent magnet in response to an external demagnetizing field such as an armature reaction in a DC machine using the main magnetic pole 3 and the auxiliary magnetic pole 4 according to the method of the present invention. The residual magnetic flux density of the permanent magnet used in the main magnetic pole 3 is B _r , the coercive force is H _c and iH _c , and the B-H characteristic and 4πI-H characteristic are the B-H curve and 4πI-H curve shown in the figure, respectively. As shown in If the operating line determined by the total magnetic resistance of the magnetic circuit of this DC machine is P _c , then in the case of the method of the present invention, the magnetic resistance at the air distance d, which accounts for most of the above total magnetic resistance, is small, so the above operation The angle θ of the line P _c with respect to the magnetic flux density B is small, and the P _c curve is B-
The magnetic flux density that intersects with the H curve at point A is B _d1 , and the point on the 4πI-H curve that corresponds to point A is point B.

Next, if a demagnetizing field ΔH acts due to the armature reaction accompanying the rotation of the armature 5, the permanent magnet operating line will remove the demagnetizing field via A→B→C→D along the arrow in the figure. After that, it returns to point A along the B-H curve, so the magnetic flux density does not change from Bd ₁ . In other words, irreversible magnetism does not occur.

On the other hand, in the case of the conventional method as shown in Fig. 1, the angle θ of the operating line P _c with respect to the B axis as shown in Fig. 4 is large because the air distance is large, and the angle θ between P _c and B-H is large. The curve intersects at point a, the magnetic flux density at this time is Bd ₂ , and the point corresponding to point a on the 4πI-H curve is b. The operating line P _i ′ and 4πI are obtained by translating the operating line P _i passing through points o and b by the armature reaction ΔH.
The intersection point with the -H curve is c, and the B-H corresponding to c
If the point on the curve is d, the d point is on the downward curve of the B-H curve, so after the demagnetizing field is removed via the d point, the operating point is not on the B-H curve but on the It moves to point a', which is different from point a, on the motion line _Pc through the path d-a' indicated by the middle arrow. Therefore, the initial line of motion
The magnetic flux density Bd ₂ for point a on P _c is
Moving on to Bd ₃ , irreversible demagnetization occurs by the difference between Bd ₂ and Bd ₃ . Such irreversible demagnetization can be prevented by the present invention.

[Brief explanation of drawings]

Figures 1 and 4 are a cross-sectional view and excitation operation analysis diagram of a conventional magnet field type DC motor, respectively.
FIGS. 2 and 3 show a cross-sectional view and an excitation operation analysis diagram, respectively, of a magnet field type DC motor according to an embodiment of the present invention. 1...Stator, 2...Yoke, 3...Main magnetic pole, 4
... Auxiliary magnetic pole, 5 ... Armature, d ... Sky distance,
δ...Grinding thickness.

Claims (1)

[Scope of Claims] 1. A main magnetic pole made of a permanent magnet and an auxiliary magnetic pole made of a magnetic material are arranged adjacent to each other in the circumferential direction of the annular inner diameter surface of the yoke, and the auxiliary magnetic pole is placed on the side of the increasing field of armature reaction. In a magnet field type DC motor in which the main magnetic pole is provided with a fixed magnetic pole, the inner diameter of the main magnetic pole is
A magnet field type DC motor characterized in that D _p is a smaller diameter than the inner diameter D _s of the auxiliary magnetic pole. 2. In the method of manufacturing a magnet field type DC motor in which a main magnetic pole made of a permanent magnet and an auxiliary magnetic pole made of a magnetic material are arranged adjacent to each other in the circumferential direction of the annular inner diameter surface of a yoke to form a fixed magnetic pole, A main magnetic pole formed with a grinding allowance δ on the inner diameter is placed in parallel with the auxiliary magnetic pole and fixed to the inner diameter surface of the yoke, and then the grinding allowance δ is adjusted to a position where the inner diameter D _p is smaller than the inner diameter D _s of the auxiliary magnetic pole. A method for manufacturing a magnet field type DC motor characterized by forming the main magnetic pole by grinding.